Technical Field
The present invention relates to optical communications and, more particularly, to the use of space division multiplexing in elliptical multimode fibers.
Description of the Related Art
As the demand for data bandwidth has increased, data transmission technologies have struggled to keep up. Current technologies stretch into transmission rates in the 100 Gbit/s range, with 400 Gbit/s and greater speeds on the horizon.
There are several technologies employed to increase the transmission rate in optical data transmissions. One example is coherent detection, which enables the use of several different kinds of modulation and multiplexing. However, transmission formats that rely on coherent detection necessitate the use of coherent transmitters and receivers whose cost and complexity may be prohibitive. One application for 100 Gbit/s and 400 Gbit/s optical fiber communications is inter- and intra-data-center connections (e.g., distances greater than 500 m and less than 100 km).
Other approaches include simple increases in the symbol speed and number of amplitude levels, but these quantities cannot be increased indefinitely. In another approach, multiple fibers may be used to multiply the transmission rate of a single fiber. However, this provides an obvious increase in the expense of transceivers, as an additional transponder will be needed for each fiber. Similarly, wavelength division multiplexing puts multiple wavelengths of light onto a single fiber but necessitates the use of multiple different light sources. In another approach, the two polarizations of a standard single mode optical fiber are used to double the data speed of an optical fiber. However, this can involve costly and complex digital signal processing, such as “multiple-input-multiple-output.”